**Transient and Persistent Gastric Microbiome: Adherence of Bacteria in Gastric Cancer and Dyspeptic Patient Biopsies after Washing**

**Malene R. Spiegelhauer 1,\*, Juozas Kupcinskas 2,3, Thor B. Johannesen 4, Mindaugas Urba 2,3, Jurgita Skieceviciene 3, Laimas Jonaitis 2, Tove H. Frandsen 1, Limas Kupcinskas 2,3, Kurt Fuursted 4 and Leif P. Andersen 1**


Received: 21 April 2020; Accepted: 13 June 2020; Published: 16 June 2020

**Abstract:** *Helicobacter pylori* is a common colonizer of the human stomach, and long-term colonization has been related to development of atrophic gastritis, peptic ulcers and gastric cancer. The increased gastric pH caused by *H. pylori* colonization, treatment with antibiotics or proton pump inhibitors (PPI) may allow growth of other bacteria. Previous studies have detected non-*Helicobacter* bacteria in stomach biopsies, but no conclusion has been made of whether these represent a transient contamination or a persistent microbiota. The aim of this study was to evaluate the transient and persistent bacterial communities of gastric biopsies. The washed or unwashed gastric biopsies were investigated by cultivation and microbiota analysis (16S rRNA gene-targeted amplicon sequencing) for the distribution of *H. pylori* and other non-*Helicobacter* bacteria. The number of cultured non-*Helicobacter* bacteria decreased in the washed biopsies, suggesting that they might be a transient contamination. No significant di fferences in the bacterial diversity were observed in the microbiome analysis between unwashed and washed biopsies. However, the bacterial diversity in biopsies shown *H. pylori*-positive and *H. pylori*-negative were significantly di fferent, implying that *H. pylori* is the major modulator of the gastric microbiome. Further large-scale studies are required to investigate the transient and persistent gastric microbiota.

**Keywords:** gastric microbiota; transient; persistent; culture; microbiome; sequencing; *Helicobacter pylori*
